Sent to Collection Lawyers without a valid reason

I have 2 cars with Netsar trackers and with 2 debit orders active. Nestar decided to stop debiting the latest car (Mini Cooper S) account and then sent me sms saying my account has been forwarded to collection lawyers Blake & Associates who have been calling me no stop for the past month and each time I ask the consultant to explain why I'm owing Netstar, they aren't able to give me an answer. I've also called Netstar call centre and each time they promise to investigate the matter & get back to me and they never do. They have my account number and my consent to debit my account but they aren't. I don't mind paying what I owe them but I need to understand how it came about that I'm owing them. They also need to rectify the issue as I opted for a debit order for a reason. I don't want the inconvenience of making EFT's.